Electrical machine

ABSTRACT

An electrical machine comprises: a first rotor, rotatable about a first axis, and having a first arrangement of magnets on a first surface thereof; a second rotor, held with a first surface thereof adjacent the first surface of the first rotor and such that it cannot rotate about the first axis, but is rotatable about a second axis, and having a second arrangement of magnets on the first surface thereof; wherein the first and second arrangements of magnets are such that rotation of the first rotor about the first axis causes rotation of the second rotor about the second axis. The first rotor is in the form of an at least partial hollow torus, with the first surface thereof being an internal surface. The second rotor is in the form of a cylinder, located within the hollow torus, with the first surface thereof being an external surface, such that the second axis is perpendicular to the first axis.

RELATED APPLICATIONS

This application is a national stage application of International patentapplication no. PCT/GB09/051121 filed Sep. 3, 2009. This applicationalso claims priority to Great Britain Patent Application No. 0816248.9,filed Sep. 5, 2008.

This invention relates to an electrical machine, and in particular to amachine that can be used to generate electrical current efficiently froma slowly moving body.

Electrical machines in the form of generators are very well known, inwhich a primary source of energy is used to rotate a body, and thisrotor cooperates with a stator to produce an electric current. However,where the primary source of energy is one of the common sources ofrenewable energy, such as wind, tide, or wave, the rotor typically movesrather slowly, at least compared with the 3000 rpm achieved in aconventional power station.

The effect of this relatively slow movement is that the generator mustbe relatively large, which in turn means that the cost and mass of thegenerator is high. If conventional mechanical gearing is used to convertthe slow rotation into a faster rotation of a rotor in a generator, thenthe gearing is a source of losses due to friction, and also reduces thereliability.

According to a first aspect of the present invention, there is providedan electrical machine, comprising:

a first rotor, rotatable about a first axis, and having a firstarrangement of magnets on a first surface thereof;

a second rotor, held with a first surface thereof adjacent the firstsurface of the first rotor and such that it cannot rotate about thefirst axis, but is rotatable about a second axis, and having a secondarrangement of magnets on the first surface thereof;wherein the first and second arrangements of magnets are such thatrotation of the first rotor about the first axis causes rotation of thesecond rotor about the second axis.

For a better understanding of the present invention, and to show how itcan be put into effect, reference will now be made, by way of example,to the accompanying drawings, in which:—

FIG. 1 is a schematic diagram, illustrating a part of a machine inaccordance with the present invention.

FIG. 2 shows a part of the machine of FIG. 1, to a larger scale.

FIG. 3 is a cross-sectional view through the part shown in FIG. 2.

FIG. 4 shows a first arrangement of magnets on the surfaces of the firstand second rotors in the machine of FIG. 1.

FIG. 5 shows a second alternative arrangement of magnets on the surfacesof the first and second rotors in the machine of FIG. 1.

FIG. 6 shows a third alternative arrangement of magnets on the surfacesof the first and second rotors in the machine of FIG. 1.

FIG. 7 shows another aspect of the arrangement of magnets on thesurfaces of the first and second rotors in the machine of FIG. 1.

FIG. 8 shows an alternative concave section cylinder form of the secondrotor.

FIG. 9 shows a second alternative arrangement of the first and secondrotors.

FIG. 10 shows an alternative convex section cylinder barrel form of thesecond rotor.

FIG. 11 shows a third alternative arrangement of the first and secondrotors.

FIG. 12 shows a fourth alternative arrangement of the first and secondrotors.

FIG. 13 illustrates a further machine in accordance with the invention,having a wheeled support for the second rotors.

FIG. 14 shows a first arrangement of a linear generator in accordancewith the present invention.

FIG. 15 shows a second arrangement of a linear generator.

FIG. 16 shows a cross section of a linear generator.

FIG. 17 shows a cross section of an alternative linear generator.

FIG. 18 shows a wave energy converter incorporating a generator inaccordance with the present invention.

FIG. 1 shows the general structure of an electrical machine 8 inaccordance with the present invention. The electrical machine isdescribed herein in the form of a generator, in which a rotation of abody is used to generate electrical power. However, it will beappreciated by the person skilled in the art that the same principle canbe used to construct a motor, in which electrical power is applied, andused to cause a body to rotate.

The machine 8 of FIG. 1 has a first rotor 10, which is connected to anaxle 12 by a support structure in the form of spokes 14. Rotation of theaxle 12 then causes the rotor 10 to rotate about the axis defined by theaxle. The rotation of the axle 12 can be driven by a power source suchas a wind turbine, a tidal current machine, or a wave energy converter,and although it can of course be driven by any power source, the machineof the present invention is particularly suitable for situations wherethe driving rotation is at a relatively low speed, for example at about20 rpm for the case of a typical 1.5 MW wind turbine. In addition,although FIG. 1 shows the rotor 10 being driven through the axle 12, itcan be driven directly by a body that is being caused to rotate by theexternal power source. For example, it may be mounted directly onto thehub of a wind turbine.

The rotor 10 is generally toroidal. That is, it has an annular shape,which can be generated by rotating a circle about an axis that lies inthe plane of the circle but outside the circle. This axis is then theaxis about which the rotor is caused to rotate.

However, the surface of the rotor is not a complete torus. Specifically,the part of the circular cross-section that lies furthest away from theaxis of rotation is omitted, leaving an annular gap 16.

Visible through the gap 16 in FIG. 1 is a cylindrical second rotor 18,which has an outer circular cross-section that is slightly smaller thanthe inner circular cross-section of the rotor 10.

FIG. 2 shows in more detail the part of the machine 8 in the region ofthe second rotor 18. Specifically, the second rotor 18 (and each of theother second rotors, not shown in FIG. 1 or 2) is mounted on a supportstructure 20, which makes it unable to move in the direction of rotationof the first rotor 10, but allows it to rotate about an axis 22 of itsown circular cross-section.

Located within the second rotor 18 is a stator 24. As is well known, thesecond rotor 18 and the stator 24 can be designed such that rotation ofthe second rotor 18 about its axis 22 causes an electrical current to begenerated in the stator 24, which can be supplied through outputelectrical circuitry (not shown) to electrical power supply lines,electrical power storage devices, etc.

FIG. 3 is a cross-sectional view through the first rotor 10, secondrotor 18, and stator 24.

As mentioned above, the first rotor 10 is rotatable about an axis thatlies in the plane of this cross-section. Meanwhile, the second rotor 18is prevented from rotating about the axis of rotation of the firstrotor, but is able to rotate about the axis 22. Provided on a first,inner, surface 26 of the first rotor 10, and on a first, outer, surface28 of the second rotor 18 are arrangements of magnets that have theeffect that, as the first rotor 10 is caused to rotate about its axis ofrotation, the second rotor 18 is forced to rotate about the axis 22.This will be described in more detail below.

In addition, provided on a second, inner, surface 30 of the second rotor18 and on a first, outer, surface 32 of the stator 24 are thearrangements that are required such that rotation of the second rotor 18about its axis 22 causes an electrical current to be generated in coilsof wire mounted on the stator 24. Suitable forms of these arrangementswill be well known to the person skilled in the art, and will not bedescribed further herein.

FIG. 4 shows a first possible arrangement of magnets on the surfaces 26,28 of the first and second rotors. It will be apparent that thearrangements are the same, but are displaced from each other. Inaddition, it will be noted that the arrangements are shown hereschematically as if the two surfaces are planar, rather than circular.The illustrated section of the surface 26 has a first magnet 34, madefrom permanent magnet material magnetized in a first direction, then apiece of iron 36, then a second magnet 38, made from permanent magnetmaterial magnetized in a second direction opposite to the firstdirection, then a second piece of iron 40, then a third magnet 42, madefrom permanent magnet material magnetized in the first direction.

The illustrated section of the surface 28 has a first magnet 44, madefrom permanent magnet material magnetized in the second direction, thena piece of iron 46, then a second magnet 48, made from permanent magnetmaterial magnetized in the first direction, then a second piece of iron50, then a third magnet 52, made from permanent magnet materialmagnetized in the second direction.

In this case, the arrangement of magnets on the surfaces 26, 28 has apitch p equal to the width of two of the magnets plus two of the piecesof iron, as shown in FIG. 4.

FIG. 5 shows a second possible arrangement of magnets on the surfaces26, 28 of the first and second rotors. Again, it will be apparent thatthe arrangements are the same, but are displaced from each other, and itwill be noted that the arrangements are shown here schematically as ifthe two surfaces are planar, rather than circular.

In FIG. 5, the illustrated section of the surface 26 has a first magnet54, made from permanent magnet material magnetized in a first direction,then a second magnet 56, made from permanent magnet material magnetizedin a second direction opposite to the first direction, then a thirdmagnet 58, made from permanent magnet material magnetized in the firstdirection, then a fourth magnet 60, made from permanent magnet materialmagnetized in the second direction, and so on. A piece of ferromagneticmaterial, for example iron, 62 is connected to one end of each of thesemagnets 54, 56, 58, 60.

The illustrated section of the surface 28 has a first magnet 64, madefrom permanent magnet material magnetized in the second direction, thena second magnet 66, made from permanent magnet material magnetized inthe first direction, then a third magnet 68, made from permanent magnetmaterial magnetized in the second direction, then a fourth magnet 70,made from permanent magnet material magnetized in the first direction,and so on. A piece of ferromagnetic material, for example iron, 72 isconnected to one end of each of these magnets 64, 66, 68, 70.

In this case, the arrangement of magnets on the surfaces 26, 28 has apitch p equal to the width of two of the magnets as shown in FIG. 5.

FIG. 6 shows a third possible arrangement of magnets on the surfaces 26,28 of the first and second rotors. Again, it will be apparent that thearrangements are the same, but are displaced from each other, and itwill be noted that the arrangements are shown here schematically as ifthe two surfaces are planar, rather than circular.

In FIG. 6, the illustrated section of the surface 26 has permanentmagnet material 82 magnetized in such a way as to produce a successionof North and South poles at the surface 26 as shown and very littlemagnetic field on the opposite surface 83, in an arrangement known as aHalbach array to a person skilled in the art.

The illustrated section of surface 28 has permanent magnet material 92magnetized in such a way as to produce a succession of magnetic Northand South poles at the surface 28 as shown and very little magneticfield on the surface 93, again forming a Halbach array.

Again, the arrangement of magnets on the surfaces 26, 28 has a pitch pequal to the distance between two successive North poles, or between twosuccessive South poles, as shown in FIG. 6.

Whether the magnets are as shown in FIG. 4, or as shown in FIG. 5, or asshown in FIG. 6, they produce a degree of coupling between the firstrotor 10 and the second rotor 18. It is also possible to use anarrangement of magnets which is based on a mixture of the schemesoutlined in FIGS. 4, 5 and 6. For instance a machine could be designedbased on the magnets at surface 28 of FIG. 6 co-operating with themagnets shown at surface 26 of FIG. 5.

It is also possible to produce the magnetic field at surfaces 26 or 28by using conventional electrical machine windings.

FIG. 7 shows in more detail the arrangements of the magnets on thesurfaces 26, 28. Specifically, the magnets are arranged in helicalpatterns. These helical patterns have the effect that rotation of thefirst rotor 10 about its axis of rotation causes rotation of the secondrotor 18 about its perpendicular axis of rotation. It is impossible toprovide identical helices on surfaces 26 and 28 for the case of thetorus and cylinder but this is not necessary.

From a stationary position, in which the arrangements of magnets havesettled into positions in which the attraction between the magnets ofopposite poles and the repulsion between the magnets of the samepolarity is maximized, rotation of the first rotor 10 about its axis ofrotation causes rotation of the second rotor 18 about its axis ofrotation (since it is unable to move with the first rotor about the axisof rotation of the first rotor) in order to maintain a position in whichthis attraction is maximized. In addition, the fact that the secondrotor has a rotational radius that is much smaller than the rotationalradius of the first rotor causes a gearing effect.

If the first rotor moves a peripheral distance equal to the pitch p ofthe magnetic helix, for example as shown in FIG. 4, 5 or 6, the secondrotor rotates a full 360 degrees. For example, if the first rotor 10 hasan outside diameter of 5 m and the second rotor 18 has an outsidediameter of around 0.5 m, a gear ratio of around 150:1 (that is, thesecond rotor rotates 150 times for each rotation of the first rotor) maybe advantageous. The gear ratio can be altered by changing the diameterof the first rotor and/or of the second rotor, by changing the pitch pof the magnets, or by using more starts on the helical thread patterns.

There is thus provided an electrical machine that can convert relativelyslow rotation efficiently into a faster rotation that can be used moreconveniently for generating electrical power.

Although one basic structure has been illustrated, it will beappreciated that other structures are possible.

FIG. 8 shows an alternative form of the first and second rotors. Asdiscussed above with reference to FIG. 1, the first rotor 10 is in theform of a torus, from which the part of the circular cross section thatlies furthest from the axis of rotation is omitted, leaving an annulargap 16. Stated alternatively, the first rotor 10 is in the form of acircumferentially-sliced torus, such that a cross section of the torusforms an arc and an annular gap 16 across a radially outer portion ofthe torus. In the embodiment shown in FIG. 8, the second rotor 18 a isnot in the form of a right circular cylinder, but rather is acylindrical object formed by rotating a curved line about the axis 22.In particular, it may be advantageous to arrange for a concave surface,as illustrated in FIG. 8, as that conforms more closely to the surfaceof the inside of the first rotor 10.

FIG. 9 shows a further alternative form of the first and second rotors,in which the first rotor 110 forms an incomplete torus in which the partof the circular cross section that lies nearest to the axis of rotationis omitted, leaving an annular gap 116, with the second rotor 118 beingvisible through this gap. Stated alternatively, the first 110 is in theform of a circumferentially-sliced torus, such that a cross section ofthe torus forms an arc and an annular gap 116 across a radially innerportion of the torus. In this case the second rotor might advantageouslybe formed by rotating a curved line about the axis 22 so as to form abarrel shaped body with a convex surface as illustrated in more detailin FIG. 10, as in this case that shape conforms more closely to thesurface of the inside of the first rotor 10.

FIG. 11 shows a further alternative arrangement, in which the firstrotor 120 is formed in the shape of an incomplete torus having two sidepieces 122, 124, by omitting the part of the torus's circular crosssection that lies nearest to the axis of rotation of the first rotor andalso the part of the circular cross section that lies furthest from theaxis of rotation. Stated alternatively, the first rotor 120 is in theform of a doubly-sliced torus, the torus being sliced along oppositefaces of a disk centered in the torus's midplane to form the twoconcentric side pieces 122, 124, a first side piece 122 and a secondside piece 124, positioned on first and second portions, respectively,of the torus's circular cross section. The second rotor 126 is heldbetween the two parts 122, 124.

FIG. 12 shows a further alternative arrangement, in which the firstrotor 130 is formed in the shape of an incomplete torus having two parts132, 134, by retaining only the part 132 of the circular cross sectionthat lies nearest to the axis of rotation and the part 134 of thecircular cross section that lies furthest from the axis of rotation,while omitting two annular side pieces. Stated alternatively, the firstrotor 130 is in the form of a doubly-sliced torus, the torus beingsliced along opposite sides of a rectangular shape centered in thetorus's circular cross section and perpendicular to the midplane of thetorus, thereby forming annular gaps between radially inner and outersurfaces thereof. The second rotor 136 is held between the two parts132, 134.

In order to illustrate the advantages of the invention, an outlinedesign of a 6.5 MW wind turbine generator is provided, based on thearrangement of first and second rotors 110, 118 as shown in FIG. 9. Inthis example, the first rotor 110 has an outside diameter of 5 m, and arotational speed of 16 rpm (revolutions per minute). There are sixteensecond rotors 118, each having an outside diameter of 0.5 m and a lengthof 0.4 m, and having a rotational speed of 2800 rpm. The active parts ofthis device have a total mass of 9 T (tonnes). This can be compared withthe estimated total mass of the active parts of a conventional directdrive permanent magnet 6.5 MW wind turbine rotating at 16 rpm, which isaround 42 T. It also compares favourably with that of an existingexperimental 5 MW wind turbine (built by Repower), which has anasynchronous doubly fed generator, operating at a speed of 670-1170 rpmdriven by a mechanical gearbox, in which the gearbox has a mass of 63 Tand the generator has a mass of 17 T.

In most rotating or linear electrical machines, it is important tomaintain a small mechanical clearance between moving parts. If this isto be done in the case of a large electrical machine, it often meansthat the mass of supporting structure, used to impart rigidity, but notelectromagnetically active, is increased. The mass problem can bealleviated in the case of the present invention by allowing thestructure to be relatively light and flexible, while maintaining thenecessary clearances by using wheels to support the second rotors,running on tracks which are attached to the first rotor.

FIG. 13 shows a machine of this type. The first and second rotors 110,118 are of the type shown in FIG. 10, in which the first rotor 110 formsan incomplete torus in which the part of the circular cross section thatlies nearest to the axis of rotation is omitted, and the second rotor118 is barrel-shaped. The second rotor 118 is mounted on a supportstructure 120, which allows it to rotate about an axis 122.

The required clearance between the first and second rotors 110, 118 ismaintained by a structure in which rails 124, 126 are provided on theouter surface of the first rotor 110. In this case, the rails 124, 126each have a rectangular profile.

Connected to the axle 122 above the second rotor 118 is a mechanism 127comprising a first rod 128, which is at 90° to the axle 122, and isconnected to a second rod 130 at an angle of about 90°. Connected tothis second rod 130 are three wheels 132, 134, 136. The first wheel 132is located so that it can run along a surface 138 of the rail 126 thatis perpendicular to the outer surface of the first rotor 110. The secondwheel 134 is located so that it can run along a surface 140 of the rail126 that is parallel to the outer surface of the first rotor 110. Thethird wheel 136 is located so that it can run along a surface (notvisible in FIG. 13) of the rail 126 that is perpendicular to the outersurface of the first rotor 110 and opposite the surface 138. A similarmechanism 142 is connected between the axle 122 above the second rotor118 and the rail 124. Further similar mechanisms 144, 146 are connectedbetween the axle 122 below the rotor 118 and the rails 126, 124respectively.

The invention has been described so far with reference to a machine inwhich the initial motion is rotational. However, a similar structure ispossible where the initial motion provided by the primary energy sourceis linear, rather than rotational. For example, some sources ofrenewable energy give rise to a reciprocating linear motion, such asthat found in many wave energy converters. If the first rotor shown inFIG. 1 above is replaced by a straight tube, which is driven by thisreciprocating linear motion, then this movement can be converted intorotation, and hence used to generate electrical power.

A machine, suitable for use as a generator in this situation, is shownin FIG. 14. A first tube 184 is connected to a primary source of energy,such that it is driven along its axis in a reciprocating linear motion,as shown by the arrows A. Provided on the inner surface 186 of the tube184 is a helical arrangement of magnets 188, 190. The tube 184 ismounted around a second smaller cylinder 180. Provided on the outersurface 192 of the tube 180 is a helical arrangement of magnets 194,196.

As a result of the interaction between the two helical arrangements ofmagnets, similar to that described above, the reciprocating linearmotion of the tube 184 is converted into reciprocating rotation in thesmaller cylinder 180 as shown by the arrows B.

A rotor (not shown, but well understood by the person skilled in theart) can than be mounted on the cylinder 180 so as to cooperate with astationary stator to generate electrical power.

FIG. 15 shows an alternative arrangement, which is identical to thatshown in FIG. 14, except that the cylinder 180 is driven along its axisin a reciprocating linear motion by a primary source of energy, as shownby the arrows C, and this movement is converted into reciprocatingrotation in the tube 184, as shown by the arrows D. A rotor (not shownin FIG. 15) can be mounted on the tube 184 so as to cooperate with astationary stator to generate electrical power.

FIG. 16 is a cross section through the machine of FIG. 15, also showingthe arrangement for generating electrical power. Specifically, a rotorpart 198 of a generator is mounted on the outside of the tube 184, andthis is located within the stator part 200 of the generator. Thus, asthe cylinder 180 reciprocates as shown by the arrows C, the cylinder 184will rotate, with changes in the rotational direction, and electricalpower can be generated.

All of the embodiments so far have referred to electrical machines inthe form of generators, where movement is converted to output electricalpower. The same structures, with appropriate changes to the electricalconnections as will be apparent to the person skilled in the art, canalso be used as electric motors. Thus, for example, in the case of thestructure shown in FIGS. 15 and 16, a linear motor may also be realised,if electrical power is provided to the stator 200, causing the rotor 198to rotate, and hence causing the cylinder 180 to move along its axis.

As described above, the embodiments shown in FIGS. 14 and 15 areintended for use in situations where the primary energy source is areciprocating motion, and will usually produce a reciprocating motion onthe output side. If continuous rotation in one direction of the rotor198 is required, however, this is also possible.

FIG. 17 shows a modification of the arrangement shown in FIG. 16, whichis arranged to produce a more continuous output power.

In this arrangement, as before, a first tube 184 is mounted around asecond smaller cylinder 180. Provided on the inner surface 186 of thetube 184, and on the outer surface 192 of the tube 180, are helicalarrangements of magnets (not shown in FIG. 17).

In this case, there are two rotors 202, 302 mounted on the outside ofthe tube 184, but they are not directly driven by the tube 184. Rather,two sprag clutches 204, 304 are connected to the tube 184, and drive therotors 202, 302. The two rotors 202, 302 then co-operate with stators201, 301 respectively, to produce electrical power as described above.The sprag clutches (or any other similar device, which could bemechanical, hydraulic, electromechanical and so on) have the propertythat they produce a positive drive to a load in one direction, but willallow the load to overrun if the rotational speed of the load is greaterthan the input rotational speed. These clutch arrangements will be wellknown to the person skilled in the art, and will not be describedfurther herein.

When the machine is being driven by a reciprocating motion of thecylinder 180, the magnetic gearing between the cylinder 180 and tube 184will cause the tube 184 to rotate, alternating between opposite firstand second rotational directions as the cylinder 180 reciprocates.

While the tube 184 is rotating in the first direction, it can drive therotor 202 through the sprag clutch 204, which allows drive in the firstdirection and allows the rotor 202 to overrun in the second direction.While the tube 184 is rotating in the second direction, it can drive therotor 302 through the sprag clutch 304, which allows drive in the seconddirection and allows the rotor 302 to overrun in the first direction.

In this way, the rotors 202 and 302 can act as flywheels to store energywhile the cylinder 180 is stationary, so being able to deliver moreconstant electrical power.

Also, the stators 201, 301 can be arranged so that the electrical outputis in a convenient form.

The machine shown in FIG. 17 may be modified for the case in which thereciprocating energy source consists of a power stroke in a firstdirection and a weaker return stroke in a second direction opposite tothe first direction. This situation could occur for instance where abuoy floating in the sea pulls a chain attached to the tube 180providing the power stroke and a spring provides the return stroke. Inthe machine of FIG. 17, the stator 301, rotor 302 and sprag clutch 304could be omitted. The sprag clutch 204 then drives the rotor 202 roundon the power stroke and allows the rotor 202 to overrun on the returnstroke.

FIG. 18 shows a further modification of the machine, allowing thesmoothing of the output power, even in circumstances where the inputenergy, in the form of the reciprocating motion, is not constant. Forexample, if a machine in accordance with the invention were to be usedas part of a sea wave energy converter, it would be preferable if theelectrical output from the device were reasonably smooth, despite thefact that typically the pattern of sea waves is not regular. In theembodiment of the invention shown in FIG. 18, means are provided tostore energy in the converter in order to smooth out variations in inputpower.

As before, a first tube 184 is mounted around a second smaller cylinder180. Provided on the inner surface 186 of the tube 184, and on the outersurface 192 of the tube 180, are helical arrangements of magnets (notshown in FIG. 17).

The arrangement is described here with reference to a situation in whichreciprocating linear motion of the cylinder 180 is converted to rotationof the tube 184, as described above with reference to FIG. 15, althoughit will be appreciated that similar arrangements can be provided in theother embodiments of the invention described above.

The rotating tube 184 can be mechanically coupled, for example via ashaft or mechanism 403 to a hydraulic pump 401. The hydraulic pump 401then drives a hydraulic motor 404 which will in turn drive an electricalgenerator 405. In this case, the fluid flow path between the hydraulicpump 401 and the hydraulic motor 404 is provided with at least onehydraulic accumulator 406. Energy storage is thus provided by thehydraulic accumulator 406 so that, even though the varying supply ofenergy to the cylinder 180 means that the tube 184 will not be rotatingat a constant speed, the fluctuations will be smoothed by the effect ofthe hydraulic accumulator, so that the output of the electricalgenerator will be more nearly constant.

As mentioned above, similar arrangements can be provided in the cases ofthe embodiments of the invention. For example, the tube 184 can be heldagainst rotation, and the cylinder 180 can thus be caused to rotate. Inthis case, the smoothing effect can be achieved by coupling the pump 401to the cylinder 180.

There are thus described various electrical machines, in the form ofgenerators and electric motors, in which an input motion of a firstcomponent is converted to an output motion of a second component, withthe first and second components being coupled together by means of amagnetic gearing.

Although the magnetic gearing is thus described in the context ofelectrical machines, the same magnetic gearing mechanisms can be used inother situations, for example where the gearing mechanism is used tochange the speed of some other type of machine. For example, in thearrangement shown in FIG. 1, the second rotors could incorporatehydraulic motors or pumps or compressors, and may not have anyelectrical context.

The invention claimed is:
 1. An electrical machine, comprising: agenerator, configured to generate electrical power, the generatorcomprising: a first rotor, rotatable about a first axis, and having afirst arrangement of magnets on a first surface thereof; a second rotorin the form of a hollow cylinder, held with a first surface thereofadjacent the first surface of the first rotor and such that it cannotrotate about the first axis, but is rotatable about a second axis, andhaving a second arrangement of magnets on the first surface thereof; anda stator located within the hollow cylinder with coils of wireconfigured to generate electrical power; wherein the first and secondarrangements of magnets are such that rotation of the first rotor aboutthe first axis causes rotation of the second rotor about the secondaxis.
 2. The electrical machine of claim 1, wherein: the first rotor isin the form of an at least partial hollow torus, with the first surfacethereof being an internal surface; the second rotor is located withinthe hollow torus, with the first surface thereof being an externalsurface, such that the second axis is perpendicular to the first axis.3. The electrical machine of claim 2, wherein the first rotor is in theform of the at least partial hollow torus extending fully around thefirst axis, but extending only partially around the second axis.
 4. Anelectrical machine, comprising: a generator, configured to generateelectrical power, the generator comprising: a first rotor, rotatableabout a first axis, and having a first arrangement of magnets on a firstsurface thereof; a second rotor, held with a first surface thereofadjacent the first surface of the first rotor and such that it cannotrotate about the first axis, but is rotatable about a second axis, andhaving a second arrangement of magnets on the first surface thereof; anda stator located within the second rotor with coils of wire configuredto generate electrical power; wherein the first and second arrangementsof magnets are such that rotation of the first rotor about the firstaxis causes rotation of the second rotor about the second axis. whereinthe first rotor is in the form of a circumferentially-sliced torus, suchthat a cross section of the torus forms an arc and an annular gap acrossa radially outer portion of the torus.
 5. An electrical machine,comprising: a generator, configured to generate electrical power, thegenerator comprising: a first rotor, rotatable about a first axis, andhaving a first arrangement of magnets on a first surface thereof; asecond rotor, held with a first surface thereof adjacent the firstsurface of the first rotor and such that it cannot rotate about thefirst axis, but is rotatable about a second axis, and having a secondarrangement of magnets on the first surface thereof; and a statorlocated within the second rotor with coils of wire configured togenerate electrical power; wherein the first and second arrangements ofmagnets are such that rotation of the first rotor about the first axiscauses rotation of the second rotor about the second axis, wherein thefirst rotor is in the form of a circumferentially-sliced torus, suchthat a cross section of the torus forms an arc and an annular gap acrossa radially inner portion of the torus.
 6. An electrical machine,comprising: a generator, configured to generate electrical power, thegenerator comprising: a first rotor, rotatable about a first axis, andhaving a first arrangement of magnets on a first surface thereof; asecond rotor, held with a first surface thereof adjacent the firstsurface of the first rotor and such that it cannot rotate about thefirst axis, but is rotatable about a second axis, and having a secondarrangement of magnets on the first surface thereof; wherein the firstand second arrangements of magnets are such that rotation of the firstrotor about the first axis causes rotation of the second rotor about thesecond axis, wherein the first rotor is in the form of a doubly-slicedtorus, the torus being sliced to form only two pieces concentric withthe first axis, where the two pieces are positioned at two differentaxial locations forming an annular gap between the two pieces in anaxial direction with respect to the first axis.
 7. An electricalmachine, comprising: a generator, configured to generate electricalpower, the generator comprising: a first rotor, rotatable about a firstaxis, and having a first arrangement of magnets on a first surfacethereof; a second rotor, held with a first surface thereof adjacent thefirst surface of the first rotor and such that it cannot rotate aboutthe first axis, but is rotatable about a second axis, and having asecond arrangement of magnets on the first surface thereof; wherein thefirst and second arrangements of magnets are such that rotation of thefirst rotor about the first axis causes rotation of the second rotorabout the second axis, wherein the first rotor is in the form of adoubly-sliced torus, the torus being sliced to form only two piecesconcentric with the first axis, where the two pieces are positioned attwo different radial locations forming an annular gap between the twopieces in a radial direction with respect to the first axis.
 8. Theelectrical machine as claimed in any one of claims 2 to 7, comprising aplurality of said second rotors, held spaced apart within the hollowtorus at predetermined positions around the first axis.
 9. Theelectrical machine of claim 1, wherein: the first arrangement of magnetson the first surface of the first rotor comprises a helical arrangement;and the second arrangement of magnets on the first surface of the secondrotor comprises a corresponding helical arrangement.
 10. The electricalmachine of claim 1, in the form of a wherein the second rotor and thestator are positioned relative to each other such that rotation of thesecond rotor about the second axis causes an electrical current to begenerated.
 11. An electrical machine, comprising: a generator,configured to generate electrical power, the generator comprising: afirst rotor, rotatable about a first axis, and having a firstarrangement of magnets on a first surface thereof; a second rotor in theform of a hollow cylinder, held with a first surface thereof adjacentthe first surface of the first rotor and such that it cannot rotateabout the first axis, but is rotatable about a second axis, and having asecond arrangement of magnets on the first surface thereof; and a statorlocated within the hollow cylinder with coils of wire configured togenerate electric power; wherein the first and second arrangements ofmagnets are such that rotation of the first rotor about the first axiscauses rotation of the second rotor about the second axis; and whereinthe first and second arrangements of magnets each comprise repeatedsequences of: a first magnet formed from permanent magnet materialmagnetized in a first direction parallel to the respective firstsurface; a first piece of ferromagnetic material; a second magnet formedfrom permanent magnet material magnetized in a second direction parallelto the respective first surface and opposite to the first direction; anda second piece of ferromagnetic material.